When I try to execute it I get a dump at the second append that states:

ITAB_ILLEGAL_SORT_ORDER
A line is to be inserted or changed at position 1 in the sorted
internal table (type SORTED_TABLE)
"\PROGRAM=ZPROGRAM\DATA=GT_ALV[49]-FIELD_STYLE".
In doing so, the sorting sequence - determined by the table key - was
destroyed.